Electron beam vacuum tube



sept. 29, 1953 G. B. LOPER 1 Re. 23,716

ELECTRON BEAM VACUUM TUBE Original Filed March 20, 1946 T5. El,

.[:i INVENToR. G50/Q65 .f5 OPER 7g/W AT Amary Reissued Sept. 29, 19.53

ELECTRON BEAM VACUUM TUBE George B. Loper, Dallas, Tex., assignor, by mesne assignments, to Socony-Vacuum Oil Company, Incorporated, New York, N. Y., a corporation of New York Original No. 2,545,822, dated March 20, 1951, Se-

rial No. 655,664, March Z0, 1946. Application for reissue September 13, 1951, Serial No.

11 Claims.

The present invention relates to a vacuum tube, and more particularly to a vacuum tube structure which provides a variable mu constant average anode current characteristic.

In seismic prospecting systems, the amplier isset for maximum gain so that the direct seismie wave produced by a charge of explosive in a shot hole produces a sharp break in the seismogram as a resultl of the initial movement of the oscillographic element. The sharp break in the seismogram thus produced by the high gain or the amplifier eliminates the necessity of estimating the precise instant at which the oscillographic element rst began to move. Subsequently, the gain of the ampliiier is reduced to a relatively low level for the reception of an initial series of reflected waves which are of higher amplitude than succeeding waves. In the application of gain control to such amplifiers and seismographic systems, it has been found that the change of the gain of the amplier introduces a corresponding modulation or distortion of the seismic wave signals transmitted. In the application of gain control to amplifiers in radio receivers, the audio or radio frequencies of the signals are relatively high compared to the low frequency of the automatic gain control voltage. In seismographic recording, the seismic signals are relatively low in frequency and have a frequency comparable to that of the gain control voltage. In radio receivers, a simple lte-r arrangement Will substantially eliminate the unwanted gain control signal from the output, but such simple filter circuits will not eliminate the undesired gain control signal eiect on the am- L pliler output in a seismographic apparatus.

In amplifiers of the type under consideration having circuits which are commonly of the resistance-capacitance coupled type, the change in gain or signal control introduces modulation of the signal by the change of potential of the interstage coupling capacitor. When the gain of the amplier is sharply reduced, the voltage of the anode circuit changes potential with regard to ground due to the sudden plate current reduction through the anode impedance or resistor. This produces a change of potential upon the coupling capacitor which then is charged through the grid coupling resistor of the succeeding stage. capacitor through the resistor of the succeeding stage drives the grid of the succeeding vacuum tube sufficiently away from normal bias as to introduce distortion and in some instances to substantially block the transmission signals.

This charging of the coupling' Matter enclosed in heavy brackets appears in the original patent but-forms nopart of this reissue specification; matter printed in italics indicates the additions made by reissue.

If the change in gain control produced no appreciable change in the anode current, the cou-.- pling capacitor would be maintained at a substantially constant average potential throughout al1 gain variations. This condition may be obtained in accordance with the present invention by the construction of a vacuum tube having a variable mu substantially constant anode current characteristic.

It is therefore an object of the present invention to provide an improved vacuum tube for ampliers which does not introduce into the signal output any components corresponding to the gain control voltage,

it is a further object of the present invention to provide an improved vacuum tube of the electron beam type having a variable mu constant average anode current characteristic.

Other and further objects of the present nvention subsequently Will become apparent by reference to the following description taken in conjunction with the accompanying drawing in which:

Fig. l diagrammatically illustrates the internal construction of one form of vacuum tube having the desired characteristics;

Fig. 2 is another diagrammatic represents.- tion of a suitable form of vacuum tube having the desired operating characteristics;

Fig. 3 is another View similar to Fig. 2 illustrating the operation of the vacuum tube under different conditions;

Fig. 4 is a circuit diagram of an ampliner utilizing a vacuum tube having a construction of the type shown in Figs. 2 and 3;

Fig. 5 shows another vacuum tube arrangement and circuit therefor; and

Fig. 6 is another diagrammatic representation of still a diierent form of vacuum tube having the operating characteristics of the present invention.

The vacuum tube having the characteristic of a constant plate current irrespective of the gain control voltage applied thereto is diagrammatically illustrated in Fig. 1. This vacuum tube has a cathode II which has on either side electron beam forming plates I2 so as normally to direct electron beams in opposite directions toward a pair of grids I3 and I4. The grids are surrounded by a pair of circumferentially con.- tinuous concentric screen grid structures I5 and I6. A cylindrical suppressor grid II is interposed between the screen grid I6 and a cylindrical anode I8 enclosed in a glass envelope 30. Positioned between the signal or control grids I3 and I4 and the cathode II are a pair of gain control rods I 9 and 2l. When there is no potential applied to the gain control rods IS and 2| the electron beam 22 will impinge upon the control grids I3 and III. When, however, a negative potential is applied to the control rods I9 .and 2I the electron beams are deilected to either side so that the gain control rods I9 and 2| cast an electron shadow upon the signal grids I3 and I4. Dependent upon the magnitude of the potential applied to the gain control rods I3 and 2I, the size of the shadow will change so that a greater or lesser amount of the energy of the electron beam 22 reaches the signal grids I3 and I4.

The electron beam 22 is not appreciably diminished by potentials appearing upon the gain control rods I9 and 2l so that the number of electrons reaching the anode I8 remain constant, thereby providing a constant plate current characteristic. The variation or potential on the gain control rods I9 and 2l, however, varies the grid plate transconductance so that the vacuum tube has a variable mu characteristic. By proper design, the gain control rods I9 and 2I may be positioned so that with a certain negative bias thereon practically none of the electrons of the electron beam 22 will reach the signal grids I3 and Id, thus making it possible to control the signal output of the vacuum tube between a maximum value and a minimum value which is substantially zero.

Figs. 2 and 3 show another construction of a vacuum tube having a variable mu constant anode current characteristic. This structure of the vacuum tube has a cathode 23 partially surrounded by an electron beam Aforming structure 2d which permits electron beams to move in two opposite directions toward a cylindrical anode 25. Adjacent the cylindrical anode 25 there is provided a suppressor grid 25. Two screen grid structures 21 and 28 [are] provideijd] a screened zone for a set of signal grids and a set of non-signal grids. Between the screen grid structures 2l and 28 in the path of the electron beams, there are located a pair of signal grids 23. In the same radius of the signal grids 29, there are located a pair of non-signal grids 3l. Between the signal grids 29 and the cathode 23. there are located two gain control rods 32. When there is no potential applied to the rods 32 relative to the cathode 23, the electron beams 33 cover the signal grids 29 and pass on to the anode 25. When a suiiiciently negative potential is applied to the gain control rods 32, the electron beams 33 will become forked or bifurcated as illustrated in Fig. 3 so that substantially no electron beam energy impinges upon the signal grids 29. The non-signal grids 3|, however, are in the path of the portions of the electron beam 33 so that the electrical and mechanical impedance presented to the electron beam under the condition of a negative potential upon the gain control rods 32 is the same as under the conditions represented by Figure 2. Thus, the impedance presented to the electron beams does not change under different conditions of gain control so that the anode current is constant.

A suitable circuit for the vacuum tube of the type illustrated in Figs. 2 and 3 is shown in Fig. 4. A pair of input terminals 38 are provided for the reception of seismic wave signals such as obtained from a suitable source which might be a, geophone. One of the terminals 38 is grounded and the other terminal is connected to a `coupling capacitor 39 which is connected to a signal grid 2S. The signal grid 29 is provided with a grid coupling resistor 4I which is connected to ground. The non-signal grid 3| is provided with a similar grid coupling resistor 42 also connected to ground. The cathode of the vacuum tube may be self-biased by a resistor 43 which is by-passed by a capacitor M. The electron beam forming element or structure 24 is connected to ground. The gain control electrodes or rods 32 are connected to ground through a resistor 45 to which may be applied the gain control voltage obtained from a suitable source 40. The screen grid structures 2l and 28 are connected to a suitable source of potential. The suppressor grid 25 is connected to the cathode 23 of the vacuum tube. The anode of the vacuumtube 25 isconnected to the source of potential through an anode coupling resistor 45. Suitable output terminals 41 are provided, one of which is connected to the anode of the vacuum tube by a capacitor 4B.

In the circuit shown in Fig. 4, the coupling point A which is the juncture between the anode resistor it and the coupling capacitor 48 remains at a constant average potential irrespective of the gain control signal applied to the resistor 45. In the circuits heretofore employed in amplifiers, a variation of the gain control voltage on an electrode of the conventional vacuum tube had the effect of changing the anode current so that the potential at the point A changed appreciably. This change in the potential at the point A would require a charging or discharging of the capacitor 48 through the grid coupling resistor of the succeeding stage. Due to the time constant of such charging circuit, the grid of the succeeding stage would be held at a different potential from the normal value for a certain time interval, and in some instances where a great change in the gain is being brought about, the grid of the succeeding stage may be driven so far from normal as to greatly distort or substantially block the transmission of seismic Wave signals.

From the foregoing it is apparent that a gain control element can be utilized to deflect an electron beam away from the signal grid and that another path for the electron beam may be provided which has the same impedance so that the anode current remains substantially constant. Another form of vacuum tube structure operating in the same manner is illustrated in Fig. 5 wherein there is provided a vacuum tube 49 having a cathode 5I provided with an electron beam focusing element 52. The beam focusing element 52 may be connected to ground, and the cathode 5I may be self-biased by a resistor 53 which is bypassed by a capacitor 5d. The vacuum tube has an anode 55 which is coupled by a capacitor 56 to an output terminal. The anode 55 is connected through an anode circuit resistor 5l to a suitable source of potential. A suppressor grid 58 located adjacent the anode 55 is connected to the cathode 5I. The screen grid structure 59 sur,- rounds a pair of grids. One 4grid 6I serves as a signal grid and the other grid 52 serves as a non-signal grid. The signal grid 6I is connected by a coupling capacitor S3 to one terminal of a pair of signal input terminals E4. The grid BI is provided with a grid circuit resistor 65 which is connected to ground. The non-signal grid 62 is provided with a similar grid resistor 65- also connected to ground. Between the cathode 5I and the ,grids 5.9, 6I and 62 there are located a pair of deflectin-g plates El and 68. These deflec'tin'g plates are connected to a gain control voltage 40 so that the plates shift the direction of an electron beam 69 either upwardly or downwardly as seen in the circuit diagram of Fig. 5. When the beam is deiiected upwardly by suitable potential upon the plates 5l and 58, the principal energy of an electron beam passes through the signal grid B I. When the beam is deected to a similar 'position downwardly, the electron beam does not strike the signal grid 6I but passes through the non-signal grid 62. At intermediate positions, the electron beam S9 will engage portions of both of the grids El and 62. Thus, a gain control potential may be applied to the vacuum tube 19 to change in one sense the engagement of Athe electron beam with the signal grid 61 while changing by an equal amount and in an 'opposite sense the engagement of the beam 'with the non-signal grid '62 to maintain substantially constant the signal potential at the point A of the anode circuit which is coupled by the capacitor 56 to the succeeding stage of amplification.

Still another vacuum tube structure operating in accordance with the principles of the present invention is illustrated in Fig. 6 wherein the vacuum tube is provided with a cathode 'H surrounded by an electron beam forming structure 12. An envelope 'i3 surrounds a cylindrical anode 14. A suppressor grid 'l5 is located concentric to the anode 14. Suitable screen grid structures 76 and 'i1 are provided to surround a pair of signal grids 18 and a pair of non-signal grids 19. Surrounding the envelope 13 is an electromagnetic coil 8|. An application of a control voltage to the magnetic coil BI will cause a displacement of an electron beam 82 much in the manner illustrated in Fig. 6. The degree of deflection may vary from the maximum illustrated in the figure to zero so that all or no part of the electron beam impinges upon the pair of signal grids 18. Since the impedance presented to the electron beam path of the electron beam 82 is constant at all times, the constant anode current will flow and yet with respect to the signal grid the tube will have a variable mu characteristic.

While the foregoing vacuum tube arrangements have for the purpose of illustration been described as being particularly adapted for the requirement of gain control in seismographic amplifiers, it is to be understood that such vacuum tubes have many other applications. For example, the vacuum tube might be used in a balanced modulator using a single-ended resistance-capacitance coupling capable of -operating at a wide range of frequencies and which would incorporate all the advantages of modulators of the prior art which, however, have required the use of push-pull circuits and transformer couplings. In explaining the operation and structure of the vacuum tubes, it furthermore has been convenient to designate one of the grids as a signal grid and the other .grid as a non-signal grid, but it will be appreciated that different signals might be applied to each of the grids as is often the case in communication systems. For example, it may be desired to fade from one signal channel to another as in the case of radio or television communication. In still other instances, it might be desirable to establish a particular balance between the levels of two signals applied to the grids. The particular balance selected might control the circuit to cause the application of the gain control voltage to apply a corrective or compensating effect 6 in accordance with the difference 'in signal levels 4on the two sets of grids.

While for the purpose of explanation of the present invention certain specic embodiments and structural arrangements have been shown in the drawing, it is to be understood that the invention is not 'to be limited thereby since such variations in the elements employed and in their arrangements are contemplated as may be vcommensurate with the spirit and scope of the invention defined inthe following claims.

What is claimed is:

[1. An electron beam vacuum tube having a cathode, electron beam forming means, a signal grid, a screen grid, a suppressor grid, an anode, and electrostatic means between said cathode 'and Vsaid signal grid lfor deilect'ing the electron beam 'away froi'n said signal grid while maintaining said anode current substantially constant] [2. An electron beam vacuum tube having an anode, two grids located equidistant from the cathode, electron beam-forming means, and electrostatic means intermediate said cathode and said grids for deecting the electron beam through a range extending from one of said grids to the other without substantial change of said anode current] [3. A vacuum tube having an anode, a suppressor grid, a cathode, means for forming an electron beam, two grids located eduidist'ant from the cathode, a screen grid, and an electrostatic electrode located between said cathode and said two grids inthe normal path of the electron beam-] [4. A vacuum tube having a cathode, an anode, a suppressor grid, a screen grid, two grids located equidistant from the cathode, means for forming an electron beam, and electrostatic plates within said tube and between said cathode and said grids for deflecting the electron beam from one grid vto the other or" said two grids] [5. A vacuum tube having an anode, a cathode, a suppressor grid, a screen grid, two grids located equidistant from the cathode, means forming an electron beam, and electrostatic means Within said tube for deflecting the electron beam from one grid to the other of said two grids] [6. A vacuum tube having an anode, a cathode, a suppressor grid, a screen grid, a signal grid and a non-signal grid respectively located equidistant from the cathode, means for forming an electron beam, and means for deflecting the electron beam from one grid to the other of said grids to change the proportion rof said beam aiected by said signal grid, said means including a pair of electrostatic plates positioned between said beam-forming means and said grids] [7. An electron beam vacuum tube having an anode, two grids located equidistant from the cathode, Vand means disposed between said cathode and said grids for deflecting the path of the electron beam from one grid to another thereby to produce relative to vone of the grids a variable transconductance characteristic without varying substantially said anode current of said tube] [8. An electron beam vacuum tube having a cathode, an anode, means for forming an electron beam between them, a signal grid having a structure through which electrons may pass interposed in the path of said beam, and structure within said tube between said cathode and said signal grid adjacent said beam for delecting said electron beam away from said signal vgrid upon application of a potential to said structure,

the anode current remaining substantially constent for any degree of deecton of said beam] 9. An electron beam vacuum tube having a cathode, an anode, electron beam forming means for establishing an electron beam between said cathode and said anode, a suppressor grid adiacent said anode, a pair of screen grids, a signal grid and a non-signal grid disposed between said screen grids, said signal grid and non-signal grid being equidistant from said cathode but electricallg insulated one from the other, and electrostatic means between said cathode and that one of said screen grids on the cathode side of said signal for changing the position of the electron beam relative to said signal grid and nonsignal grid to change in one sense the engagement of said beam with said signal grid while simultaneously changing in the opposite sense and by an equal amount the engagement of said beam with said non-signal grid.

10. An electron beam vacuum tube having a cathode, a single anode, two screen grids adiacent said anode, electron beam forming means for establishing an electron beam between said cathode and said anode, a signal grid and a nonsignal grid disposed between said screen grids, said signal grid and said non-signal grid being equidistant from said cathode but electrically insulated one from the other, and means intermediate said cathode and said screen grids for de- Jlecting said electron beam through a range emtending ,from one of said grids to the other without substantial change of said anode current.

11. A vacuum tube having a cathode, an anode, a suppressor grid adjacent said anode, electron beam ,forming means for establishing an electron beam between said cathode and said anode, a pair of screen grids, two control grids loca-ted equidistant from said cathode and intermediate said screen grids, and an electrostatic electrode located between said cathode and said screen grids in the normal path of the electron beam to change in one sense the engagement of said beam with one of said control grids while simultaneously changing in the opposite sense and by an equal amount the engagement of said beam with the other of said control grids.

12. A vacuum tube having a cathode, a single anode, a pair of screen grids forming a screened zone between said anode and said cathode, electron beam forming means for establishing an electron beam between said cathode and said anode, two control grids located equidistant from said cathode and in said zone and electrically insulated one from the other, and electrostatic plates within said tube and between said cathode and said screen grids for deftecting said electron beam from one control grid to the other to change in one sense the engagement of said beam with a first of said control grids while simultaneously changing in the opposite sense and by an equal amount the engagement of said beam with the other of said control grids.

13. A vacuum tube having a cathode, an an.- ode, a suppressor grid adjacent said anode, a

pair of screen grids positioned between said cathode and said suppressor grid to establish a screened zone, two control grids located equidistant from said cathode in said screened zone, means for forming an electron beam between said cathode and said anode, and electrostatic means within said tube for deflecting the electron beam lfrom one of said contro-l grids to the other.

14. A vacuum tube having a cathode, an anode, a suppressor grid adjacent said anode, a pair of screen grids intermediate said cathode and said suppressor grid for establishing a screened zone, two control grids located equidistant from said cathode in said screened zone, electron beam forming means for establishing an electron beam between said cathode and said anode, and means for deflecting said electron beam from one control grid to the other control grid to change the proportion of said beam ejected by said control grids, said means including a pair of electrostatic plates positioned between said electron beam forming means and said screen grids.

15. An electron beam vacuum tube having a cathode, a single anode, a pair of screen grids for establishing a screened zone between said cathode and said anode, two control grids located equidistant from said cathode and disposed in said zone between said screen grids, and means disposed between said cathode and said screen grids for deflecting the path of the electron beam from one control grid to another thereby to produce relative to one of the control-grids a variable transconductance characteristic without varying substantially the anode current of said tube.

16. An electron beam vacuum tube having a cathode, a single anode, means for forming an electron beam between them, a pair of circumferentially continuous screen grids for establishing a screened zone between said cathode and said anode, a signal grid having a structure through which said electrons may pass interposed in said zone intermediate said screen grids in the path of said beam, and structure within said tube between said cathode and said screen grids adjacent said beam for deflecting said beam away from said signal grid upon application of a potential to said structure, the anode current remaining substantially constant for any degree of deflection of said beam.

17. A vacuum tube having a cathode, a single anode, a pair of cylindrical screen grids forming a screened zone between said anode and said cathode, electron beam forming means ,for establishing an electron beam between said cathode and said anode, two control grids located equidistant from said cathode and in said zone and electrically insulated one from the other, and electrostatic plates within said tube and between said cathode and said screen grids for deylecting said electron beam from one control grid to the other to change in one sense the engagement of said beam with a rst of said control grids while simultaneously changing in the opposite sense and by an equal amount the engagement of said beam with the other of said control grids.

18. An electron beam vacuum tube having a cathode, a single anode, a pair of cylindrical screen grids for establishing a screened zone between said cathode and said anode, two control grids located equidistant from said cathode and disposed in said zone between said screen grids, and means disposed between said cathode and said screen grids for defleoting the path of the electron beam from one contro-Z grid to another thereby to produce relative to one of the control grids a variable transconductance characteristic without varying substantially the anode current of said tube.

`19. A vacuum tube comprising a cathode, a pair of cylindrical screen grids forming a screened zone between them, electron beam-forming means for establishing an electron beam between said cathode and said screen grids, two control grids located equidistant from said cathode and in said 9 screened zone and electrically insulated one from the other, electrostatic plates within said tube and between said cathode and said control grids for defteeting said electron beam from one of them to the other to change in one sense the engagement of said beam with a yrst of them while simultaneously changing in the opposite sense and by an equal amount the engagement of said beam with the other of them, and an anode circumferentially coetensive with the etent of deflection of said beam ,for receiving said electron beam in all positions relative to said grids, whereby upon deflection of said beam relative to said control grids the average value of said anode current remains constant,

GEORGE B. LOPER.

References Cited in the le of this patent or the original patent UNITED STATES PATENTS Number Number 

